// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// For atomic operations on reference counts, see atomic_refcount.h.
// For atomic operations on sequence numbers, see atomic_sequence_num.h.

// The routines exported by this module are subtle.  If you use them, even if
// you get the code right, it will depend on careful reasoning about atomicity
// and memory ordering; it will be less readable, and harder to maintain.  If
// you plan to use these routines, you should have a good reason, such as solid
// evidence that performance would otherwise suffer, or there being no
// alternative.  You should assume only properties explicitly guaranteed by the
// specifications in this file.  You are almost certainly _not_ writing code
// just for the x86; if you assume x86 semantics, x86 hardware bugs and
// implementations on other archtectures will cause your code to break.  If you
// do not know what you are doing, avoid these routines, and use a Mutex.
//
// It is incorrect to make direct assignments to/from an atomic variable.
// You should use one of the Load or Store routines.  The NoBarrier
// versions are provided when no barriers are needed:
//   NoBarrier_Store()
//   NoBarrier_Load()
// Although there are currently no compiler enforcement, you are encouraged
// to use these.
//

#ifndef BASE_ATOMICOPS_H_
#define BASE_ATOMICOPS_H_

#include <stdint.h>

// Small C++ header which defines implementation specific macros used to
// identify the STL implementation.
// - libc++: captures __config for _LIBCPP_VERSION
// - libstdc++: captures bits/c++config.h for __GLIBCXX__
#include <cstddef>

#include "base/base_export.h"
#include "build/build_config.h"

#if defined(OS_WIN) && defined(ARCH_CPU_64_BITS)
// windows.h #defines this (only on x64). This causes problems because the
// public API also uses MemoryBarrier at the public name for this fence. So, on
// X64, undef it, and call its documented
// (http://msdn.microsoft.com/en-us/library/windows/desktop/ms684208.aspx)
// implementation directly.
#undef MemoryBarrier
#endif

namespace base {
namespace subtle {

    typedef int32_t Atomic32;
#ifdef ARCH_CPU_64_BITS
// We need to be able to go between Atomic64 and AtomicWord implicitly.  This
// means Atomic64 and AtomicWord should be the same type on 64-bit.
#if defined(__ILP32__) || defined(OS_NACL)
    // NaCl's intptr_t is not actually 64-bits on 64-bit!
    // http://code.google.com/p/nativeclient/issues/detail?id=1162
    typedef int64_t Atomic64;
#else
    typedef intptr_t Atomic64;
#endif
#endif

    // Use AtomicWord for a machine-sized pointer.  It will use the Atomic32 or
    // Atomic64 routines below, depending on your architecture.
    typedef intptr_t AtomicWord;

    // Atomically execute:
    //      result = *ptr;
    //      if (*ptr == old_value)
    //        *ptr = new_value;
    //      return result;
    //
    // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value".
    // Always return the old value of "*ptr"
    //
    // This routine implies no memory barriers.
    Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
        Atomic32 old_value,
        Atomic32 new_value);

    // Atomically store new_value into *ptr, returning the previous value held in
    // *ptr.  This routine implies no memory barriers.
    Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value);

    // Atomically increment *ptr by "increment".  Returns the new value of
    // *ptr with the increment applied.  This routine implies no memory barriers.
    Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment);

    Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
        Atomic32 increment);

    // These following lower-level operations are typically useful only to people
    // implementing higher-level synchronization operations like spinlocks,
    // mutexes, and condition-variables.  They combine CompareAndSwap(), a load, or
    // a store with appropriate memory-ordering instructions.  "Acquire" operations
    // ensure that no later memory access can be reordered ahead of the operation.
    // "Release" operations ensure that no previous memory access can be reordered
    // after the operation.  "Barrier" operations have both "Acquire" and "Release"
    // semantics.   A MemoryBarrier() has "Barrier" semantics, but does no memory
    // access.
    Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
        Atomic32 old_value,
        Atomic32 new_value);
    Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
        Atomic32 old_value,
        Atomic32 new_value);

    void MemoryBarrier();
    void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value);
    void Acquire_Store(volatile Atomic32* ptr, Atomic32 value);
    void Release_Store(volatile Atomic32* ptr, Atomic32 value);

    Atomic32 NoBarrier_Load(volatile const Atomic32* ptr);
    Atomic32 Acquire_Load(volatile const Atomic32* ptr);
    Atomic32 Release_Load(volatile const Atomic32* ptr);

// 64-bit atomic operations (only available on 64-bit processors).
#ifdef ARCH_CPU_64_BITS
    Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
        Atomic64 old_value,
        Atomic64 new_value);
    Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value);
    Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);
    Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment);

    Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
        Atomic64 old_value,
        Atomic64 new_value);
    Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
        Atomic64 old_value,
        Atomic64 new_value);
    void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value);
    void Acquire_Store(volatile Atomic64* ptr, Atomic64 value);
    void Release_Store(volatile Atomic64* ptr, Atomic64 value);
    Atomic64 NoBarrier_Load(volatile const Atomic64* ptr);
    Atomic64 Acquire_Load(volatile const Atomic64* ptr);
    Atomic64 Release_Load(volatile const Atomic64* ptr);
#endif // ARCH_CPU_64_BITS

} // namespace subtle
} // namespace base

#if defined(OS_WIN)
// TODO(jfb): The MSVC header includes windows.h, which other files end up
//            relying on. Fix this as part of crbug.com/559247.
#include "base/atomicops_internals_x86_msvc.h"
#else
#include "base/atomicops_internals_portable.h"
#endif

// On some platforms we need additional declarations to make
// AtomicWord compatible with our other Atomic* types.
#if defined(OS_MACOSX) || defined(OS_OPENBSD)
#include "base/atomicops_internals_atomicword_compat.h"
#endif

#endif // BASE_ATOMICOPS_H_
